Taste does not relate to caffeine.
Arabica has about 1% caffeine that makes it out of the dose into brewed coffee, espresso might be approx 0.60% (for shorter ratios like 1:2 1:2.5, more for longer ratios) according to Hoffmannās video on the subject.
Nero make a point of using lower caffeine content coffee.
Intensity of flavour is more related to roast level & origin (when considering Arabica).
The figures quoted above seem to me mg of caffeine, rather than mg/L, which tells you how much caffeine you get overall, but doesnāt tell us much about how that relates to caffeine concentration/drink size.